I have a very reclusive race who basically get into (usually) tedious and time consuming hobbies to occupy their time. In the event they do try to bond with someone else, they'll invite someone over and not really engage with them and continue to do whatever their hobby is.

Other members of this same race are observant and learn much about the other by what their hobby of choice is, how they do it, how meticulous they are about it, etc. This is usually deeply personal and specific to them so its a big bonding step, whereas other races usually get somewhat confused on what's going on and try to socialize instead (which interrupts the bonding process).